MIDDLE EAR PRESSURE DEREGULATION AFTER TYMPANOSTOMY TUBE INSERTION Perhaps the most well supported clinical evidence for our model of Otitis Media with Effusion (OME) pathogenesis by middle ear (ME) pressure disregulation is the documented positive effect of tympanostomy tube (TT) insertion in preventing and resolving OME episodes. Because TTs bypass the Eustachian tube (ET) to maintain ambient ME pressure, these observations suggest that adequate ME pressure-regulation and not other suggested functions of the ET is prerequisite for disease resolution. Longitudinal studies show that after TT insertion in MEs with OME, the volume of the ME airspace progressively increases which correlates with decreasing ME inflammation and effusion volume. Our mathematical model shows that these changes should be reflected as lesser rates of gas exchange across the ME mucosa which are realized as a decreased demand placed upon the ET for gas resupply. In the proposed study, we will enroll children aged 3 years and older with TTs inserted for OME and measure the ME gas demand, ME volume and ETF longitudinally between TT insertion and extrusion, and then follow the enrolled patients for disease recurrence after TT extrusion. These results will be used to test the hypotheses that: 1) gas transfer across the ME mucosa (MEM) decreases in phase with resolution of ME inflammation and effusion;2) gas transfer across the MEM is increased by an episode of otorrhea;3) ETF is unaffected by TT insertion, and 4) measurement of ETF and transMEM gas transfer (supply/demand balance) predicts disease recurrence and presentation after TT extrusion. The results of these studies will be used to support or refute tested components of our model of ME pressure-regulation and to develop test protocols for risk assignments with respect to disease recurrence in individual ears after TT extrusion.